need help with rgb to cmyk conversion

every tome i convert an image from rgb to cmyk to be printed i loose alot of my brighter colors...namely blues....i know these rich colors can be printed...(i see them all the time on flyers and magazines)...so what can i do to keep these colors...please help

don't flatten the layers

The blues in your image a probably not in the CMYK gamut range.

http://www.adobe.com/support/techguides/color/colormodels/rgbcmy.html

Look at the chart near the bottom. If it is a solid blue, try using a spot colour. There is some vibrant blues in the Pantone Spot Colours. If you are printing on a proper printer, then you have to be in CMYK mode, and on screen there will appear to be some colour lose. Another thing I do if my blues get to dull, is after I convert to CMYK, I go into the Layers and adjust my blue setting. This always helps.

Remember your monitor displays in RGB so it is obvious when you switch modes it may not look right. But it prints and looks fine, you will be surprised.